DESCRIPTION (Taken directly from the application) The primary cause of death in cystic fibrosis (CF) patients arises from pulmonary failure secondary to chronic respiratory tract infections with P. aeruginosa The broad, long term goal of this proposal is to test the efficacy of specific immunotherapy to eradicate the mucoid variants of Pseudomonas aeruginosa that chronically colonize the lungs of patients with CF. The major hypothesis being evaluated is that progression of chronic infection with mucoid P. aeruginosa in CF patients is due to a failure to produce opsonic antibodies to the major surface antigen mucoid exopolysaccharide (MEP, also commonly called alginate). Thus, providing MEP-specific opsonic antibodies to the site of infection should contribute to the eradication of mucoid P.aeruginosa from the lungs of chronically colonized CF patients. To this end we propose to generate a series of human monoclonal antibodies that mediate opsonophagocytic killing of mucoid P.aeruginosa. We will then evaluate the effect of human immunoglobulin isotype to determine which mediates the most effective opsonic killing of mucoid P.aeruginosa. To do this we will clone the variable region gene segments from the opsonic human monoclonal antibodies into vectors which have different human immunoglobulin constant region genes (IgG1-4 and IgA). The antibodies produced after transfection into, and high level production by, CHO cells will have different human constant regions responsible for the biologic activity of the antibodies and identical variable regions responsible for antigen binding. We will then evaluate the protective efficacy of the monoclonal antibodies alone and in combination in vivo using a mouse chronic lung infection model. Overall, controlling P.aeruginosa infection is a clear goal of any therapy meant to improve the care of CF patients. If effective, immunotherapy proposed here should have a major impact on the quality of life of CF patients, increase life expectancy, and decrease hospitalizations and the enormous associated costs.